Active studies are being made from various angles to develop novel compounds having an outstanding efficaciousness, and at the same time to increase the pharmacological effectiveness of these novel chemical substances or of chemical substances which have already been in use as pharmaceuticals by changing the dosage form or by optimizing the dosage regimen.
For example, with the purpose of prolongating the duration time of medicines who have a short half-life period which is regarded as the parameter for the effective duration time of medicines in the body, there have been considerable activities to develop sustained release pharmaceuticals which are made to have a concentration between the minimum effective concentration or higher and the maximum safety concentration or lower, so that the effective ingredients may be absorbed into the human body in the whole range of effective blood concentration extending over a long period of time.
As examples of sustained release pharmaceuticals, there are pharmaceutical preparations in the form of a tape or a plaster which are made to contain a prescribed amount of medicines in their adhesive layers, having a specific size (Japanese Patent Laid-Open Publication Nos. 116011/'82 and 134020/'83).
Conventional tape or plaster preparations have problems. In case where it is desired to administer a pharmaceuticals as long as possible between the minimum effective concentration or higher and the maximum safety concentration or lower, they are simply made to have an increased concentration of medicines in the adhesive layer with the result of increasing the initial concentration of medicines absorbed into the human body or causing cutaneous diseases. If the diffusion rate of the medicines is lowered by changing the composition of an adhesive compound to slow down the adsorption rate of the medicines, the initial absorption concentration of the medicines decreases.
As another method of increasing the sustained release effect of tape and plaster preparations, there is a method to increase the thickness of an adhesive compound layer; however, this method is apt to raise such problems as to increase the skin irritation or to allow part of the adhesive compound to stick to the skin as the residue.
There is another method in which the concentration of medicines in the adhesive compound is lowered while the area of the plaster stuck to the skin is made larger. This method, however, is also confronted with problems of the inconvenience in the handling of the plaster, the enlargement of the undesirable irritation of the skin, and the limit of the site of application.
As the improved type of tape or plaster preparation, tere is one whose adhesive layer is made to contain microcapsules filled with medicines (Japanese Patent Publication No. 16566/'79); however, a plaster of this type requires complicated procedures in the course of its production and the sustained release of the medicines is not satisfactory enough.
There is still another type of tape and plaster, and it is a plaster which is designed to have its hollow fibers filled with medicines and then have these hollow fibers arranged on its outer surface which comes in contact with the skin upon which it is applied (Japanese Patent Laid-Open Publication No. 31611/'82). However, problems are also apt to be found with them by causing unpleasant irritation or eruption on the skin due to the extraordinary rise of the drug concentration at the site of its application where the skin is in direct contact with the drug. The plaster of this type can not be said to have enough sustained releasing function, either.